Cushcraft has been making antennas for a very long time. I wonder if
the design of that model simply dates back to when hams were only
allowed 1 KW. Maybe nobody bothered to update the rating. The only
other reason I can think of for why a standard yagi wouldn't be able to
handle more power is if it had a gamma match with a smallish capacitor.
Almost any other feed system should handle more than a KW unless the
connections other than the SO-239 (straps, screws, etc) are really flimsy.
Dave AB7E
On 7/31/2022 6:25 AM, Lux, Jim wrote:
On 7/31/22 6:01 AM, Pete Smith N4ZR wrote:
I have just bought a small Cushcraft 3-element 6-meter yagi. Only
small fly in the ointment is that it is *only* rated at 1 KW. It
looks to me that this limitation might relate to the feedline
connection, which is a bulkhead SO-239 (mounted with a big nut)
bracketed to the center of the driven element.
My question is, do I need another connector here, or maybe insulation
between the bracket and the element? If so, what material makes
sense? Any other advice?
The rating might be derived from "only tested to 1kW"
But if it's design limited, it's either current at the feed point
(Yagis often have very low feed point resistance, which is transformed
up to 50 ohms by the matching network, or by using a folded dipole at
the feed) or voltage at the element tips (hard to model, usually
validated by testing).
1kW into 20 ohms is 7 Amps - Easily handled by a UHF connector, but
what does the rest look like?
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